Brush assembly



June 2, 1959 I F. P. vAcHA 2,889,529

BRUSH ASSEMBLY Filed March 8, 1956 lg. 4 26 2 22 I 2 24 I2 INVENTOR. 1 FRED P. VACHA ATTOR NEYS o 2,889,529 [Ce Fatented June 2, 1959 BRUSH ASSEMBLY Fred P. Vacha, Babson Park, Mass., assignor to The Gamewell Company, Newton Upper Falls, Mass., a corporation of Massachusetts Application March 8, 1956, Serial No. 570,339

7 Claims. (Cl. 338-202) The present invention relates to brush assemblies for rotary variable impedance devices.

An object of the present invention is to provide a rotary brush assembly of low cost, while yet securing the benefits of a reliable low impedance connection from a conveniently accessible fixed terminal to a movable contact on an impedance element.

A further object is to provide a brush assembly of sturdy construction, which makes and maintains good electrical contact on the impedance under severe environmental conditions, including atmospheric conditions and mechanical phenomena such as vibrations.

A still further object is to provide a brush assembly adapted for angular adjustment on the shaft, such adjustment being particularly although not exclusively useful where several brushes are supported in a specified phase relationship on a common shaft with wipers bearing upon one closed-circuit impedance, or upon each of a plurality of ganged impedances.

With the foregoing and other objects in view, a feature of the invention resides in a novel assembly including a rotor shaft, a collector ring bushing, and a collector ring mounted on the bushing. .The shaft, bushing and ring are assembled and fit together in a specific manner to provide the necessary mechanical and electrical means insulated from the shaft for connection of the fixed terminal with the movable contact on the impedance winding. By reason of the cooperative relationship of the foregoing parts, the brush assembly can be readily adjusted angularly about the rotor shaft to position the wiper with great accuracy.

Another feature resides in the simplicity of construction and the facility with which assembly of the parts can be accomplished.

Still other features of the invention reside in certain details of construction and assembly which will be evident from the following description thereof, and from the appended drawing illustrating the same.

In the drawing,

Fig. 1 is an end elevation partially broken away, of an impedance assembly incorporating a first embodiment of the invention;

Fig. 2 is a side elevation partly in section, showing ganged brush assemblies of the form illustrated in Fig. 1;

Fig. 3 is an end elevation of a variable impedance device incorporating a second form of the invention; and

Fig. 4 is a side elevation in section taken on line 4-4 of Fig. 3.

Figs. 1 and 2 illustrate what is now considered to be the preferred form of the invention. The rotor shaft 12 of the brush assembly is rotatably supported within a generally cylindrical housing 14 of insulating material such as a phenolic resin or its equivalent, which is adapted to receive and support a toroidally-wound impedance element 16. The element 16 is formed in the usual manner by winding a suitable resistance wire about a mandrel of circular cross section. It will be obvious, however, that mandrels of other cross sections may be employed alternatively. Also, it is within the scope of the invention to provide impedance elements so disposed in relation to the movable wiper contact that said contact bears axially rather than radially upon the winding, although the illustrated forms utilize radial bearing pressure in both instances.

A suitable fixed and readily accessible brush terminal 18 is threaded in the housing 14, the terminal securing and making electrical connection with one or more brush wires 20 of spring metal. The wire 20 in turn extends through a hole drilled in the housing 14 and makes sliding contact with the brush assembly as hereinafter more fully described.

The shaft 12 is constructed of a suitable metal, for example stainless steel, and is provided with a groove to receive a retaining ring 22 and also with straight knurls 24 adjacent the groove.

In making the brush assembly a subassembly is first formed. This consists of a bored, cylindrical, unthreaded, flanged insulating collector ring bushing 26 having appreciable resilient properties, an inside-threaded metallic collector ring 28 and a metallic collector ring extension 30. The extension 30 bears a wiper arm 32 of spring metal strip secured thereto by spot welding or the like. The arm 32 has a portion near its end shaped to receive a short length of wire constituting a wiper 34, the wiper being soldered to the arm and bearing resiliently upon the winding 16.

The collector ring 28 is provided with an annular concave groove 36 upon which the brush wire 20 is adapted to bear, and is further provided with a shoulder to receive the extension 30. The collector ring and extension are securely fastened together by upsetting the shoulder as illustrated at 38 while supporting the collector ring in a suitable jig.

The clearance inside the threads of the collector ring is equal to, or preferably slightly greater than, the outer diameter of the bushing 26 (exclusive of the flange) prior to assembly of the collector ring therewith. it should be noted that, prior to assembly of the parts, the bushing 26 has no external threads, being formed with smooth cylindrical surfaces both inside and out. The subassembly of the bushing with the collector ring is accomplished by simply sliding the collector ring loosely over the cylindrical portion of the bushing until the grooved end of the ring rests against the flanged portion of the bushing.

While the subassembly is thus held together it is forcefitted upon the shaft 12 over the knurls 24. The bore in the bushing 26 has an interference fit with the knurled portion of the shaft, that is, the clearance through the bushing is less than the clearance around the knurls. As a result, in force-fitting the subassembly onto the shaft the resilient bushing 26 is deformed radially so as to enter the threads 40 in the collector ring as illustrated in Fig. 2, and also the knurls. Thus the assembly of the parts upon the shaft assures a tight fit between the shaft and the bushing on the one hand, and between the bushing and the collector ring on the other hand. It should be noted that while the knurls prevent rotation of the bushing upon the shaft 12, the bushing and collector ring are threaded upon one another, whereby the application of suflicient tangential force to the wiper arm 30, while holding the shaft 12 fixed, permits rotary adjustment of the wiper in relation to the shaft. Since the bushing is of resilient material, the flange does not appreciably impede such adjustment in either direction within a sizeable angular range depending upon the pitch of the threads 40.

In Fig. 2 there is also illustrated a second brush assembly 42 identical with that described above, this assembly having a brush 4 extending from a fixed terminal 4-6. This latter terminal is supported in a housing 48 identical with the housing 14, the housings being preferably formed to fit in nested or ganged relationship as illustrated. Suitable longitudinal bolts or screws (not shown) are provided to hold the housings together, as is conventional in such assemblies.

In the assembly of ganged impedances, it frequently occurs that a certain phase or angular relationship between the wipers is specified. Thus for example, it may be desired to provide eight identical ganged potentiometers with brushes precisely 45 apart. The present invention is well suited to this type of application since the common shaft 12, with brush assemblies mounted thereon in approximately the correct phase relation, may be supported in a suitable fixture and the wiper arms accurately rotated thereabout until precisely the correct angles are achieved. It will be understood that the torque necessary to turn a wiper arm about the rotor shaft after the assembly step described above greatly exceeds any torque contemplated in actual operation by an adequate margin.

it will be seen that in a substantially similar way one may provide one or more brushes in phased relationship bearing upon a single impedance, rather than a plurality of impedances, and that such impedance may have an open or a continuous (closed-circuit) winding, if desired.

Figs. 3 and 4 illustrate an alternative form of the invention, characterized by the fact that the brush wire bears axially upon the rotary assembly, rather than radially as in the embodiment of Figs. 1 and 2.

A suitable housing 50 supports a terminal 52 in substantially the same manner as illustrated in Figs. 1 and 2, but in this case the terminal 52 supports a looped brush wire 54 pre-formed in the shape substantially as illustrated in Figs. 3 and 4. The ends of the brush wire 54 are brought together and extended through a central bore in the terminal 52, which is thereafter crimped thereabout as illustrated at 56.

The brush assembly includes a grooved and knurled shaft 58 substantially similar to the shaft 12, the groove receiving a retaining ring 60.

A bored metallic collector ring 62 of cylindrical shape is provided with internal threads 64- and a smooth, preferably buffed surface 66 upon which the brush wire 5-;- resiliently and slidably bears at two points. A flanged insulating collector ring bushing 68 having resilient properties is formed in substantially the same way as the bushing 26, with smooth outer and inner cylindrical surfaces, the outer surface being of the same or preferably slightly smaller diameter than the clearance inside the threads 64 in the collector ring 62.

The collector ring has a wiper arm 70 of spring metal strip secured to its outer periphery by spot welding or the like, the arm 70 being formed to receive a wiper contact 72 bearing resiliently on a winding 74.

The assembly of the parts is accomplished in substantially the same way as previously described. The subassembly of the collector ring 62 and bushing 68 is first formed, and while the collector ring is held against the flange on the bushing, the bushing is forced upon the shaft 58 until the flange of the bushing comes to rest upon the retaining ring 6d.

It will be noted that in this embodiment, as in the one previously described, the collector ring bushing is necessarily resilient so as to permit its radial deformation when forced upon the rotor shaft. In this assembly operation the bushing deforms into the knurls 0n the shaft and into the threads in the collector ring. To this end, the material preferably used for the bushing is Teflon (a plastic consisting of a tetrafluoroethylene polymer), although any other suitable insulating material having corresponding resilient properties may be substituted therefor.

It will be obvious that, while a particular form of brush 4 54 has been illustrated in connection with the embodiment of Figs. 3 and 4, this brush may have other alternative shapes to change the bearing pressure or number of points of contact between the brush and the surface 66 of the collector ring 62.

From the foregoing description, it will be seen that a desirable brush assembly for a variable impedance device has been provided, the assembly having a simple form which is readily and securely fitted together, while yet providing convenient means for rotary adjustment of the wiper in relation to the rotor shaft.

It will also be seen that while the invention has been described with reference to specific embodiments thereof, various modifications of design, assembly and relationships of the parts may be accomplished by the application of skills ordinarily employed in the art without departing from the spirit and scope of the invention.

Having thus described the invention, 1 claim:

1. A rotor assembly for a variable impedance device having, in combination, a rotor shaft, a resilient, deformable insulating collector ring bushing raving a bore formed with an interference fit on said shaft, a metallic collector ring having an internal thread formed to fit closely but freely over the unassembled bushing, and a wiper secured to the collector ring, whereby said bushing enters said thread upon forcing the assembled bushing and collector ring onto the shaft, said bushing being adapted after being forced upon the shaft to permit angular threaded adjustment of the ring thereon while resisting rotation between itself and the shaft.

2. A rotor assembly for a variable impedance device having, in combination, a rotor shaft having a knurled surface, a resilient, deformable insulating collector ring bushing having a bore formed with an interference fit on said surface, a metallic collector ring having an internal thread formed to fit closely but freely over the unassembled bushing, and a wiper secured to the collector ring, whereby said bushing enters the knurls of said shaft and said thread upon forcing the assembled bushing and collector ring onto the shaft, said bushing being adapted after being forced upon the shaft to permit angular threaded adjustment of the ring thereon while said knurled surface prevents rotation between the bushing and shaft.

3. A variable impedance device having, in combination, a housing, an impedance element supported in the housing, a rotor shaft, a resilient, deformable insulating collector ring bushing having a bore formed with an interference fit on said shaft, a metallic collector ring having an internal thread formed to fit closely but freely over the unassembled bushing, a wiper secured to the collector ring and bearing resiliently on said impedance element, and a metallic brush element secured in the housing and bearing slidably and resiliently on said collector ring, whereby said bushing enters said thread upon forcing the assembled bushing and collector ring onto the shaft said bushing being adapted after being forced upon the shaft to permit angular threaded adjustment of the ring thereon while resisting rotation between itself and the shaft.

4. A variable impedance device having, in combination, a housing, an impedance element supported in the housing, a rotor shaft, a resilient, deformable insulating collector ring bushing having a bore formed with an interference fit on said shaft, a metallic collector ring having a circumferential groove and an internal thread formed to fit closely but freely over the unassetnbled bushing, a wiper secured to the collector ring and beating resiliently on said impedance element, and a metallic brush element secured in the housing and bearing slidably and resiliently on said groove, whereby said bushing enters said thread upon forcing the assembled bushing and collector ring onto the shaft said bushing being adapted after being forced upon the shaft-to permit angular threaded adjustment of the ring thereon while resisting rotation between itself and the shaft.

5. A variable impedance device having, in combination,

aseasas a housing, an impedance element supported in the housing, a rotor shaft, a resilient, deformable insulating collector ring bushing having a bore formed with an interference fit on said shaft, a metallic collector ring having a surface normal to the axis of the shaft and an internal thread formed to fit closely but freely over the unassembled bushing, a Wiper secured to the collector ring and bearing resiliently on said impedance element, and a wire brush element formed with a loop lying generally at right angles to the shaft axis, said brush element having a portion secured in the housing and a portion bearing slidably and resiliently on said surface of the collector ring said bushing being adapted after being forced upon the shaft to permit angular threaded adjustment of the ring thereon While resisting rotation between itself and the shaft.

6. The method of assembling a rotor brush assembly upon a knurled shaft which comprises the steps of assembling a metallic collector ring secured to the brush assembly and having an internal thread over an annular, deformable, insulating coilector ring bushing of slightly smaller outside diameter than said internal thread, and

6 force-fitting the bushing over the knurls of the shaft to distort the bushing radially into said internal thread.

7. The method of assembling a rotor brush assembly upon a knurled shaft which comprises the steps of securing the brush to a metallic collector ring having an internal thread, assembling the collector ring over an annular, deformable, insulating collector ring bushing of slightly smaller outside diameter than said internal thread and of smaller inside diameter than the outer diameter of the knurls on said shaft, and forcefitting the bushing over the knurls of the shaft to distort the bushing radially into said internal thread.

References Cited in the file of this patent UNITED STATES PATENTS 1,287,426 Pleister Dec. 10, 1918 2,228,770 Le Tourneau Ian. 4, 1941 2,657,295 Barclay ct. 27, 1953 2,688,681 Nyyssonen Sept. 7, 1954 FOREIGN PATENTS 657,986 reat Britain Oct. 3, 1951 

